In order to further characterize the reactivity of ACPA to citrullinated peptides, RA patient sera (n = 28), HC sera (n = 28) and MS sera (n = 10) were tested for reactivity to a citrullinated α-enolase peptide (KIHARCEIFDS-Cit-GNPTVEC) by ELISA. Here, PRTN3 is linked to rheumatoid arthritis.